Structure of trans-chloro-1,4-bis(ϱ-methoxyphenyl)-1,4-diaza-3methylbutadiene-2-yl-bis(triphenylphosphine)-palladium(II)

The structure of the compound trans-[PdCl {$\text{C(N-?-C}{}_6\text{H}{}_4\text{OMe)C}$(Me)N-?-C₆H₄OMe} (PPh₃)₂] was solved, using a conventional combination of Patterson and Fourier functions, least-squares refinements and electron density difference maps, to a reliability index R of 0.069 for the 2923 observed reflections collected by four-circle diffractometer. The palladium arom is surrounded in a roughly planar fashion by two trans phosphorus atoms, a chlorine atom, and a σ-bonded carbon atom of the diazabutadienyl group. This group assumes a trans configuration, the NCCN fragment being virtually planar and nearly normal to the mean coordination plane. The Pdligand bond lengths are: PdC 1.98(1), PdCl 2.41(1),PDP(1) 2.33(1) and PdP(2) 2.35(1) Å.     

Selenium-tellurium sequences in binary glasses as depicted by 77Se and 125Te NMR

Some resolved solid state (77)Se NMR spectra are presented in the Te(x)Se(1-x) vitreous system at ambient temperature. They exhibit three different kinds of Se lines assigned to the following Se atom neighborhoods: Se-Se-Se, Se-Se-Te, and Te-Se-Te. Different models were considered to describe the way the Se and Te atoms are linked into the chains: clustering process, homogeneous distribution, random distribution. Finally, thanks to the measurements of the relative intensities of the lines, it appears that Se and Te atoms are mainly randomly distributed with a small preference for heteropolar bonds. The (125)Te spectra are also shown but their resolution is too weak to be informative concerning the vitreous network.     

Crystal and Molecular Structure of the 4:3 Complex between Lanthanum Nitrate and Pentaethyleneglycol Dimethyl Ether

The crystal and molecular structure of [La(NO₃)₃]₄(C₁₂H₂₆O₅)₃ has been determined from low-temperature single-crystal X-ray diffraction data. The complex crystallizes in the monoclinic space group I2 with Z = 2. Lattice parameters at 150 K are a = 12.234 (6) Å, b = 11.105 (5), c = 26.613 (9), β = 90.65 (4)°. The structure was solved by Patterson and Fourier techniques and refined to a conventional R_F-value of 0.068. The compound contains three dinitrato complex cations [La(NO₃)₂C₁₂H₂₆O₆]⁺ with 10-coordinate lanthanum ions and one hexanitrato anion, [La(NO₃)₆]^3?, with a 12-coordinate La(III)-ion. One complex cation has a C₂-symmetry while the two others, which are crystallographically equivalent, have no symmetry and contain a disordered ligand molecule. The polyther adopts a ring-like conformation in all the complex moietis. The La? O(nitrate) distances lie in the ranges 2.52–2.53 and 2.49–2.62 Å, with average values of 2.53 (7) and 2.56 (6) Å, respectively, fo the species with C₂- and C₁-symmetry; the La? O(ether) bond lengths lie int he range 2.54–2.79 Å (average: 2.6 (1)) for the C₂-moiety and their mean value amounts to 2.6 (2) for the disordered species. The hexanitrate has a C₂-symmetry and the La? O distances range between 2.56 and 2.67 Å with an average value fo 2.64 (4) Å. The effective ionic radii of the 10- and 12-coordinate La(III) ions are estimated as 1.28 and 1.33 Å, respectively.     

Ruthenium(II) Complex of the Alkaloid 2-Bromoleptoclinidinone. Preparation and Interaction with Double-Stranded DNA

The fused pentacyclic alkaloid 2-bromoleptoclinidinone ( 1 ) isolated from an ascidian possesses a bidentate chelating site. Complexation of 1 with [cis-RuCl₂{(D₈)bpy}₂] · 2H₂O forms an octahedral complex which was isolated both as hexafluorophosphate 2 and chloride 3 salts. Intercalation of 3 in calf-thymus DNA was shown to occur as well as photoactivated cleavage of double-strand supercoiled DNA pBR322 under visible-light irradiation.     

Intraresidue distribution of energy in proteins

Boltzmann-like distributions appear in many properties and energy-related quantities of proteins. A few examples are hydrophobicity, various types of side-chain/side-chain interactions, proline isomerization, hydrogen bonds, internal cavities, interactions at the level of specific atom types, and the propensity of the phi/'phi' ratio. Here, we conjecture that the Boltzmann hypothesis also holds for the intra-residue energy distribution. We confirm the conjecture by calculating the energies of 41,672 residues of the structures of highly resolved proteins, where at least 12 out of 20 naturally occurring amino acids follow Boltzmann's law. We further examine the entire set of all residue energies and find that the convolution of the individual distributions gives a Poisson function, which is followed by approximately 50% of individual proteins' structures.     

Surface rheology and foaming properties of sodium oleate and C12(EO)6 aqueous solutions

The dynamic surface tension (DST) and the surface viscoelastic modulus of sodium oleate aqueous solutions at different concentrations were measured using an image analysis tensiometer based on the oscillating bubble technique. The diffusion coefficient of oleate moieties was calculated from DST measurements and the surface viscoelastic modulus using the Langmuir-Szyszkowski and the diffusion-controlled adsorption models. The viscoelastic moduli obtained from model calculations were compared with the corresponding experimental values. The diffusion coefficient of C(12)(EO)(6) in water and the parameters of the Langmuir-Szyszkowski adsorption isotherm were taken from the literature and used to calculate the surface viscoelastic modulus of its aqueous solutions at different concentrations. The foaming properties of both C(12)(EO)(6) and sodium oleate solutions, viz., the foam conductance and the water volume fraction in the foam, were measured using a commercial Foamscan device. Foaming experiments with C(12)(EO)(6) and sodium oleate solutions were carried out either under static conditions; i.e., the foam conductance and the water volume fraction were measured as a function of time after the generation of a fixed volume of foam, or under dynamic conditions; i.e., the foam conductance and the water volume fraction were measured during foam formation. The variations in the foam permeability as a function of surfactant concentration were related to the viscoelastic properties of the air/water interface and to the presence of micelles in the foam films. With foams in which the water volume fraction was higher than 0.05, the foam electrical conduction could be described using a simple parallel resistor model and their conductance measurements were related to the foam water volume fraction. The results related to water drainage under static conditions were used to interpret water drainage under dynamic conditions. Preliminary conjectures on the influence of foam permeability and water volume fraction on the yield of the flotation deinking process were drawn from these results.     

Design and Synthesis of Aviram–Ratner‐Type Dyads and Rectification Studies in Langmuir–Blodgett (LB) Films

The design and synthesis of Aviram–Ratner‐type molecular rectifiers, featuring an anilino‐substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ‐spacer bicyclo[2.2.2]octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X‐ray analysis. The photophysical properties of the TTF‐BCO‐exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir–Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current–voltage (I–V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I–V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor.